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PhD theses

Investigation of the mobility of uranium(VI) in argillaceous rock at higher salinity

PhD student:

Katharina Fritsch

Supervisors:

Prof. Dr. G. Bernhard, Dr. K. Schmeide (HZDR)

Division:

Surface processes

As well as salt domes and crystalline rock, argillaceous rock is considered as host rock for radioactive waste repositories. Suitable clay formations in Germany are located in Lower Saxony and parts of Saxony-Anhalt and Mecklenburg-Western Pomerania. Therefore the mobility of uranium – an important component of radioactive waste – in argillaceous rock must be studied. The influence of ionic strength on uranium migration must be evaluated in particular, since the pore water of North German clay has a high salt content.

Continuing earlier studies, sorption and diffusion experiments of uranium(VI) in the clay minerals illite and montmorillonite and in natural Opalinus clay from Mont Terri rock laboratory (Switzerland) will be conducted, with ionic strengths up to 3 mol/l. The experiments in illite and montmorillonite will be carried out with varying pH values to observe pH dependency, while Opalinus clay will be studied under a constant pH of 7.6. NaCl, MgCl2, CaCl2 and natural Opalinus clay pore water act as background electrolytes. The experiments will be performed both in presence and absence of organic ligands like humic acids, since these ligands can influence uranium mobility through complexation. For some of these experiments, the temperature will be varied between 10 and 60 °C. Furthermore the influence of high salinity on the weathering and leaching of clay will be studied.